closed but the 08 3 with the 2.3 has the thermostat built into the water outlet housing,so both get replaced at the same time. the housing also has a small diameter bypass tube built in to it that kept it from getting all the way hot, which was weird to me at first because it would go up about 2/3 of the way then as i drove down the road it went back down some, then back up at next light. but never got all the way to the red. so i checked the coolant level and it was fine. i babied it home then the next day went to drive it and it went up to 2/3-3/4 of the way up when it warmed up and stayed there i popped the hood and the fan was kicking with all its might so i knew the fan was ok and working at a parts store i just bought the thermostat and changed it the next morning and it was fine after that, i did a coolant flush as well. i used peak universal coolant as i cannot justify $30 a gallon for mazda fl22 coolant that lasts "10 years" when the peak universal will last 5 and costs less than half that.
